Method of continuously casting tube

ABSTRACT

A tundish receiving a first molten metal and a closed-end mold are moved apart relative to each other so that the mold forms a solidified shell of a billet, molten metal flowing through the solidified shell to the mold. During the casting, a second or altered molten metal is introduced into the tundish to flow through the elongating billet so that a continuously cast billet is produced with a core of one metal, a layer of alloyed metals, and a shell of another metal. Billets may be produced with steel cores and stainless steel shells, &#39;&#39;&#39;&#39;killed&#39;&#39;&#39;&#39; steel cores and &#39;&#39;&#39;&#39;rimmed&#39;&#39;&#39;&#39; steel shells, and other combinations. Tubing may also be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted.

[451 Aug. 1, 1972 [54] METHOD OF CONTINUOUSLY CASTING TUBE [72] Inventor: Leonard Watts, Cedarhurst, NY.

[73] Assignee: Technicon Instruments Corporation,

Tarrytown, NY.

221 Filed: Mayl3, 1971 [21] Appl.No.: 143,055

Related US. Application Data [52] US. Cl ..164/85, 164/86 [51] Int. Cl ..B22d ll/08, B22d 11/06 [58] Field of Search ..164/82, 85, 86, 273 R, 274,

[56] References Cited UNITED STATES PATENTS 2,408,514 10/1946 l-lazelett 164/85 3,542,116 ll/l970 Machlinm; ..164/86 Primary Examiner-R. Spencer Annear Attorney-Tedesco & Rockwell ABSTRACT A tundish receiving a first molten metal and a closedend mold are moved apart relative to each other so that the mold forms a solidified shell of a billet, molten metal flowing through the solidified shell to the mold. During the casting, a second or altered molten metal is introduced into the tundish to flow through the elongating billet so that a continuously cast billet is produced with a core of one metal, a layer of alloyed metals, and a shell of another metal. Billets may be produced with steel cores and stainless steel shells, killed steel cores and rimmed steel shells, and other combinations. Tubing may also be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted.

13 Claims, 9 Drawing Figures ATTORNEYS METHOD OF CONTINUOUSLY CASTING TUBE This is a continuation-in-part application of my application Ser. No. 27,607 filed Apr. 13, 1970 now U.S. Pat. No. 3,625,277, titled: CONTINUOUS CASTING PROCESS, which is a continuation-in-part of my application Ser. No. 705,491 filed Feb. 14, 1968, now U.S. Pat. No. 3,517,725, titled CONTINUOUS CASTING PROCESS AND APPARATUS, issued June 30, 1970.

BACKGROUND OF THE INVENTION It is highly desirable to produce bi-metallic billets, slabs, or the like, which have one material or metal as a core with a shell or thick coating of another metal. Many types of metals have been clad together to produce such composites, but they do not lend themselves to low cost, high tonnage applications. This invention allows for the low cost production of old and as yet unknown new types of clad or composite metals which will open up many new applications.

In a more conventional area, cold rolled, low carbon steel sheet accounts for a large portion of the steel tonnage produced. Rimmed steel accounts for a good portion of this sheet production, but rimmed steel produced by continuous casting has not been able to meet high quality standards, particularly those of the automotive industry. Rimmed steel, however made, has a high iron oxide and a low carbon content. The dissolved oxygen evolves in the form of carbonoxide gases (CO and CO Upon cooling, the carbon, sulphur and phosphorous migrate from the skin of a billet toward the center and segregate as metaloids. A heavy rim is formed at the outer skin which is markedly lower in carbon, sulphur and phosphorous. Elongated gas bubbles form just below the rim, as an effect of the cooling process. Bubbles which do not weld shut during the subsequent rolling process are usually far enough below the surface so as not to cause blemishes.

When rimmed steel is cast by conventional continuous casting techniques, gas bubbles and metaloids are trapped in the plastic zone just below the rim. Since there is no relative motion between the solidified shell and the molten core, the gas bubbles and metaloids remain at a rather shallow depth after solidification of the billet and afterwards break through the surface during rolling. These porosity and metaloid problems render continuously cast billets of rimmed steel unsaleable for purposes such as auto body steel. This invention may be used to provide continuously cast rimmed steel billets without excessive defects.

Heretofore, tubing, particularly that constructed of steel, has been made by a process which required piercing a billet and subsequently rolling the metal on a mandrel. This is a time consuming and expensive procedure.

SUMMARY OF THE INVENTION A cooled, closed-end mold and a tundish receiving molten metal are moved apart relative to each other so that the mold forms a solidified shell of a billet through which molten metal flows to the mold as the billet elongates as it is continuously cast. Melting of the shell is inhibited by a water spray. If the volume of the shell of a given billet is calculated, this volume of molten metal may be introduced into the tundish and cast. Another molten metal equal in volume to that of the core of the given billet is then introduced into the tundish. The

second metal passes behind the first metal so that substantially all of the latter flows into the mold to form the shell. Thus, when the billet is complete, the shell of the first metal is filled with a core of the second metal which then solidifies. Where the second molten metal contacts the solidified shell, an alloy layer will form.

The invention provides high tonnage 1 continuously cast billets of clad metals. It may also provide a shell of one steel about a core of a different steel. Rimmed steel may becast to form a shell and then the balance of the steel may be killed and cast to form a core.

According to the invention, tubing may be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a longitudinal, vertical section through a I fragmentary length of a billet made according to this invention;

FIG. 5 is a transverse sectional view through the billet of FIG. 4;

FIG. 6 is a longitudinal vertical section through a continuous casting apparatus, after adding a second or altered metal, illustrating a modified form of the inventionfor forming a tube, and generally similar in nature to FIG. 2;

FIG. 7 is a sectional view taken on line 7-7 of FIG.

FIG. 8 is a view generally similar to FIG. 6, illustrating a further modification of the invention wherein composite tubing is fonned; and

FIG. 9 is a sectional view taken on line 99 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a ladle 10 (not drawn to scale) pours a first molten steel 11 into a tundish 12. A starting bar 13 extends into a closed-end mold 14 having a chamber 15 through which a coolant 16 circulates. Mold l4 and tundish 12 are moved apart relative to each other at an average casting speed to continuously cast a billet as described in my U.S. Pat. No. 3,517,725 issued June 30, 1970.

As shown in FIG. 2, mold 14 forms a solidified shell 17 through which molten metal flows to the mold 14 from the relatively separating tundish l2. Nozzles 19 provide a controlled and regulated water spray to in hibit shell 17 from melting.

If a given steel billet is to be cast 3 feet wide, 12 inches thick, and about feet long, as one example, the volume of shell 17 about 1 inches thick can easily be calculated. This volume of a first molten steel 1 l is cast from ladle 10. The volume of the core of the billet can also be easily calculated. Ladle 20 contains this volume of a second molten steel 18 which is cast as shown in FIG. 2. The second molten steel 18 flows through the tundish l2 behind the first molten steel ll with an area of inter-mixing 21.

As may be seen in FIG. 3, when the contents of ladle 20 is cast, the first steel 11 has formed the length of shell 17 and the second steel 18 forms a molten core which solidifies'with'acone of solidification 25 moving in a direction from mold 14 toward tundish 12, forming core 26 of one steel and a shell 17 of another steel. After casting, the end portions of the billet 30 are separated to free the billet from the tundish and for the discard of the shortarea of intermixing 21 adjacent the moldl4. a

g In one embodiment of this invention, rimmed steel is, cast in. a volume sufficient to form a shell 17 of a billet. Sufiicient steel may remain in ladle to cast the core. This 'remaining steel is killed? by adding a suitable deoxidizensuch as aluminum, silicon, or the like, to the molten metal in ladle 10. This forms stable oxides so the core will be of a homogeneous composition. Billets of this steel will be suitable for automobile body steel and like applications as it will have all the surface qualities of rimmed steel, the drawing qualities of killed steel, and none of the conventional drawbacks of either. I i l Another embodiment of this invention would cast a shell 17 of stainless steel Type 304 and a core of carbon steel Type A.I.S.I. 1015. Cooling of shell 17 by jets or nozzles 19 would be regulatedto keep the shell 17 of uniform thickness. 7 Depending upon the combinations of steels or metals cast, the casting times, and the-cooling rates, a layer of alloy of a desired type may be formed between the shell 17 and the core 26of a billet 30. In some applications, copper, bronze, aluminum, and aluminum alloy cores may be cast in carbon or stainless the core 26."The billet 30 shown in FIGS. 4 and ,5 has a hausted in theformation of the outer shell 36. When the desired volume of the firsfmolten metal 34 has flowed through the tundish, the remaining volume, at the source, may be'modified-by alloy-addition orthe source replaced by a second liquid metal 38. j

The second molten metal 38'flows through the tundish, starting bar and the solidifiedshell 36-of the first metal. The first and second'molten metals have an intermixed area 40 thereof within the solidified shell. This intermixed area moves toward the mold 14 as the I first liquid metal is converted to solidified shell atthe steelshells. Combinations of non-ferrous metals may also, be cast. With cooling properly regulated, a core metal of a higher. melting point than a shell metal may be cast in a'billet. The term billet as used herein is intended to include slabs andother forms which may be continuously cast. v lt is highly desirable to cast hollow shapes. Casting hollow elongated shapes to form tubing eliminates the piercing step which'is well known in the conventional manufacture of seamless tubing. A modified form of casting which casts tubing of a single metal or an alloy is shown in FIG. 6. In this process, the tundish 12 or source of metal and the closed end mold 14 are separated relatively to one another along an inclined path with the mold lowermost, as illustrated in this view. Molten metal flows along a downward path from the tundish toward the mold. When the source of liquid metal in the tundish has been exhausted, relative motion of the mold and tundish continues as shown in this view. Solidified casting shell 31 continues to be produced in the mold from the'liquid metal 32 within the shell being used as the source of supply. As the castmold. The lengthening portion of the solidified shell 36 containing the second liquid metal 38 receives-an increased cooling efi'ect from the nozzles 19 to solidify the shell to a greater depth by being impinged by an increased volume of cooling water from the nozzles 19 behind the moving intermixed area 40 of the metals, that is, intermediate the intermixed area 40'and the receding level 42 of the second metal 38 in the condition shown in FIG. 8. In the last-mentioned view the level 42 is not behind the intermixed area 40.

The aforementioned technique causes a layer of the second liquid metal 38 adjacent to the solidified shell 36 of the first metal 34 tosolidify thereagainst. When the source of supply of the second liquid metal 38 in the tundish has been exhausted, relative motion of the mold and tundish continues as indicated in FIG. 8. The shell of the first metal continues to be produced at the mold as the inner solidified layer'of the second metal continues to be produced behind the moving zone 40 of intermixed liquid metal. The level 42 of I the second liquid metal in the solidified shell continuously drops until substantially all the first liquid metal has been converted to theouter shell layer and the second liquid metal to an inner shell layer or tube. The solidified outer shell 36"and the inner tubular layer of the composite tube may, though not necessarily, have the cross section shown in FIG. 9, that is generally rectangular. As shown in FIGS. 8 and 9 the inner shell or layer formed by the second metal 38 is indicated at 44. After casting, the end portions of the tube are separated to free the tube from the tundish and for the discard of the short area of intermixing 40 adjacent the mold 14.

It will be understood that in the continuous casting of tubing as aforesaid, the source of metal in the tundish need not be exhausted to form tubing but merely that the flow from this source be stopped.-

While this invention has been shown and described in the best forms known, it will nevertheless be understood that these are purely exemplary and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

l. The process of continuously casting a metal tube comprising the steps of:

a. flowing a that metal from a source of molten metal into a cooled, closed-end mold,

b. relatively moving apart the source of molten metal and the mold along an inclined path with the mold lowermost, at an average casting speed forming a solidified shell of a tube about a molten core, molten metal from the source flowing through the shell toward the mold, and after termination of the flow from the source, continuing the relative separation of the source and the mold using molten metal in the shell as a source to form additional solidified shell as the level of the source in the shell drops, leaving behind it a hollow tube while the source in the shell diminishes.

, 2. The process according to claim 1, wherein the volume of molten metal cast substantially equals the volume of the solidified tubular wall.

3. The process according to claim 1, wherein the metal is steel.

4. The process according to claim 1, wherein the thermal conductivity of the metal is substantially in the order of magnitude of steel.

5. The process of continuously casting a metal tube having an outer shell and an inner layer of different metals comprising the steps of:

a. flowing a first metal from a source of molten metal into a cooled, closed-end mold,

b. relatively moving apart the source of molten metal and the mold along an inclined path with the mold lowermost, at an average casting speed forming a solidified shell of a tube about a molten core, molten metal from the source flowing through the shell toward the mold,

c. impinging a coolant spray against the exterior of said shell,

d. terminating the flow of the first metal from said source,

e. continuing the relative separation of the source and the mold while flowing a predetermined volume of second molten metal differing from the first metal from the point of origin of said source through the solidified shell behind the first molten metal so that substantially all of the latter flows into the mold to form the outer portion of the shell and the second metal forms progressively an inner layer of the shell as the level of the source of the second molten metal in the shell drops, leaving behind it a hollow tube, and

f. concurrently with the flowing of the second metal through the shell increasing the impinging coolant spray against the exterior of the shell progressively along a path behind the diminishing level of the first metal in the shell.

6. The process according to claim 5, wherein the volume of the first molten metal substantially equals that of said outer portion of the shell, and the volume of the second molten metal substantially equals that of said inner layer of the shell.

7. The process according to claim 5, wherein the first and second metals are steels.

8. The process according to claim 5, wherein the first metal is steel and the second metal is a non-ferrous metal.

9. The process according to claim 5, wherein the first metal is stainless steel and the second metal is carbon steel.

10. The process according to claim 5, wherein the first metal is carbon steel and the second metal is stainless stefl 11. e process according to claim 5, wherein the 

1. The process of continuously casting a metal tube comprising the steps of: a. flowing a first metal from a source of molten metal into a cooled, closed-end mold, b. relatively moving apart the source of molten metal and the mold along an inclined path with the mold lowermost, at an average casting speed forming a solidified shell of a tube about a molten core, molten metal from the source flowing through the shell toward the mold, and c. after termination of the flow from the source, continuing the relative separation of the source and the mold using molten metal in the shell as a source to form additional solidified shell as the level of the source in the shell drops, leaving behind it a hollow tube while the source in the shell diminishes.
 2. The process according to claim 1, wherein the volume of molten metal cast substantially equals the volume of the solidified tubular wall.
 3. The process according to claim 1, wherein the metal is steel.
 4. The process according to claim 1, wherein the thermal conductivity of the metal is substantially in the order of magnitude of steel.
 5. The process of continuously casting a metal tube having an outer shell and an inner layer of different metals comprising the steps of: a. flowing a first metal from a source of molten metal into a cooled, closed-end mold, b. relatively moving apart the source of molten metal and the mold along an inclined path with the mold lowermost, at an average casting speed forming a solidified shell of a tube about a molten core, molten metal from the source flowing through the shell toward the mold, c. impinging a coolant spray against the exterior of said shell, d. terminating the flow of the first metal from said source, e. continuing the relative separation of the source and the mold while flowing a predetermined volume of second molten metal differing from the first metal from the point of origin of said source through the solidified shell behind the first molten metal so that substantially all of the latter flows into the mold to form the outer portion of the shell and the second metal forms progressively an inner layer of the shell as the level of the source of the second molten metal in the shell drops, leaving behind it a hollow tube, and f. concurrently with the flowing of the second metal through the shell increasing the impinging coolant spray against the exterior of the shell progressively along a path behind the diminishing level of the first metal in the shell.
 6. The process according to claim 5, wherein the volume of the first molten metal substantially equals that of said outer portion of the shell, and the volume of the second molten metal substantially equals that of said inner layer of the shell.
 7. The process according to claim 5, wherein the first and second metals are steels.
 8. The process according to claim 5, wherein the first metal is steel and the second metal is a non-ferrous metal.
 9. The process according to claim 5, wherein the first metal is stainless steel and the second metal is carbon steel.
 10. The process according to claim 5, wherein the first metal is carbon steel and the second metal is stainless steel.
 11. The process according to claim 5, wherein the thermal conductivity of the first metal is substantially in the order of the magnitude of steel and the second metal is steel.
 12. The process according to claim 5, wherein the thermal conductivity of the first metal is substantially in the order of the magnitude of steel and the second metal is a non-ferrous metal.
 13. The process according to claim 5, wherein the first metal is treated to provide the second metal. 